1. Field of the Invention
The present invention relates to an exposure apparatus.
2. Description of the Related Art
A conventional projection exposure apparatus projects a circuit pattern of a reticle (mask) onto a wafer or another substrate via a projection optical system in manufacturing fine semiconductor devices, such as a semiconductor memory and a logic circuit, using the photolithography technology.
The minimum size or a resolution transferable by the projection exposure apparatus is proportionate to a wavelength of the light used for exposure, and inversely proportionate to a numerical aperture (“NA”) of the projection optical system. The shorter the wavelength is and the higher the NA becomes, the smaller the resolution is. The resolution R of the projection exposure apparatus can be given by Equation 1 below where is a wavelength of a light source, NA is a numerical aperture of the projection optical system, and k1 is a constant determined by an optical system, a reticle, and a process:R=k1×λ/NA  Equation 1
Along with the recent demands for fine processing to a semiconductor device, use of a shorter wavelength of the exposure light is promoted. For example, use of a shorter wavelength of the ultraviolet is promoted from a KrF excimer laser with a wavelength of about 248 nm to an ArF excimer laser with a wavelength of about 193 nm. The NA of the projection optical system becomes higher with the immersion lithography that provides a NA above a theoretical limit in air of 1. The k1 factor reduces as a reticle structure, an illumination condition, and a process condition are optimized. However, as the k1 factor reduces, a reticle pattern is not precisely transferred or reproduced on a wafer due to the optical proximity effect (“OPE”).
Accordingly, it is proposed to add an optical proximity correction (“OPC”) pattern to a reticle pattern on a reticle. A more sophisticated OPC pattern has also recently been proposed that takes care of a process model in addition to the OPE correction.
Some other technologies that correct the OPE are proposed. See Japanese Patent Laid-Open No. 2000-228358. Japanese Patent Laid-Open No. 2000-228358 arranges a lens array just above a reticle, divides a reticle pattern into plural reticles so that a imaged pattern is not subject to the OPE, illuminates the reticle with spotted rays from the lens array, and performs plural exposures.
Nevertheless, prior art cannot resolve a fine pattern with a good contrast while maintaining the semiconductor manufacturing cost. For example, the sophisticated OPC pattern complicates the reticle pattern, increasing the reticle data. Hence, it takes a long time to manufacture and inspect the reticle, and the manufactured reticle pattern contains more errors and defects, remarkably increasing the reticle cost, and the semiconductor manufacturing cost.
Japanese Patent Laid-Open No. 2000-228358 needs a reticle with no OPC pattern, and can avoid an increased semiconductor manufacturing cost due to the OPC pattern, but plural exposures with different reticles still increase the semiconductor manufacturing cost.